1. Field of the Invention
The present invention relates to a fuel injection control assembly for a cylinder-injected engine for controlling fuel injection based on a mean fuel pressure acting on an injector, and in particular relates to a fuel injection control assembly for a cylinder-injected engine in which reliability is improved by calculating the mean fuel pressure to a high precision and ensuring that control and calculation track changes in the fuel pressure.
2. Description of the Related Art
Cylinder-injected engines in which an injector is disposed in a combustion chamber of an engine cylinder and fuel is injected directly into the combustion chamber are well known as referenced by Japanese Patent Laid-Open No. HEI 11-62676 and Japanese Patent Laid-Open No. HEI 11-153054, etc.
For example, the fuel injection control assembly for a cylinder-injected engine disclosed in Japanese Patent Laid-Open No. HEI 11-62676 includes a mean fuel pressure computing means for calculating the mean fuel pressure from weighted means of fuel pressure detected at times other than when the injector is injecting fuel, and correcting the length of an injection pulse which is output to the injector based on the mean fuel pressure.
The fuel injection control assembly for a cylinder-injected engine disclosed in Japanese Patent Laid-Open No. HEI 11-153054 detects fuel pressure at predetermined intervals (or in synchrony with a rotational angle of the engine) at times other than when the injector is injecting fuel.
FIG. 12 is a structural diagram schematically showing a generic fuel injection control assembly for a cylinder-injected engine.
In FIG. 12, injectors IF are disposed in each cylinder of an engine 1, the injectors IF injecting fuel directly into a combustion chamber in each cylinder.
Various sensors 2 for detecting running states and a fuel pressure sensor 12 are disposed in the engine 1. The various sensors 2 include a conventional airflow sensor, throttle sensor, crank angle sensor, etc.
Running information from the various sensors 2 and fuel pressure information PF from the fuel pressure sensor 12 are input into an electronic control unit (ECU) 20. The injectors 1F have electromagnetic solenoids activated by an injection pulse signal J from the ECU 20, the injectors 1F being opened by passing current through the solenoids.
Fuel supplied to the injectors 1F is drawn from a fuel tank 3 and adjusted to a target fuel pressure PFo in a high-pressure pipe 8. Thus, an amount of fuel proportional to the duration of the injection pulse signal J (the injection pulse duration) is injected by the injectors 1F.
Intake air is distributed to each cylinder of the engine 1 by means of an air supply pipe (not shown). An air filter, the airflow sensor, a throttle valve, a surge tank, and an intake manifold are disposed in the air supply pipe in that order from an upstream end.
Fuel (such as gasoline) in the fuel tank 3 is drawn into a low-pressure pump 4 driven by a motor 4M. Low-pressure fuel discharged by the low-pressure pump 4 is supplied to a high-pressure pump 7 via a fuel filter 5 and a low-pressure pipe 6.
A low-pressure return pipe 6A having a low-pressure regulator 9 disposed therein branches from the low-pressure pipe 6, returning to the fuel tank 3.
The high-pressure fuel pump 7 is driven by the engine 1, the rotational frequency of the high-pressure fuel pump 7 corresponding to the rotational frequency of the engine 1.
FIG. 13 is a characteristic graph showing the relationship between engine rotational frequency Ne and the discharge cycle TP of the high-pressure pump 7. Because the rotational frequency of the high-pressure pump 7 is proportional to the rotational frequency Ne of the engine, the discharge cycle TP of the high-pressure pump 7 is shortened as the engine rotational frequency Ne increases, as shown in FIG. 13.
In FIG. 12, high-pressure fuel discharged from the high-pressure pump 7 is supplied to the injectors 1F via the high-pressure pipe 8. A high-pressure return pipe 8A having a high-pressure regulator 10 disposed therein branches from the high-pressure pipe 8, a downstream end of the high-pressure return pipe 8A converging with the low-pressure pipe 6 and the low-pressure return pipe 6A.
The low-pressure regulator 9 adjusts the amount of fuel returning to the fuel tank 3 from the low-pressure return pipe 6A. The pressure of fuel supplied by the low-pressure pump 4 to the high-pressure pump 7 is adjusted to a predetermined low pressure depending on the amount of fuel returned by the low-pressure regulator 9.
The high-pressure regulator 10 is driven by an excitation current Ri (a control signal) supplied by the ECU 20, and adjusts the amount of fuel returned to the low-pressure return pipe 6A, and adjusts the actual fuel pressure PF acting on the injectors 1F to the target fuel pressure PFo.
In other words, the high-pressure regulator 10 returns fuel from the downstream side of the high-pressure fuel pump 7 to the low-pressure side by continuously changing the cross-sectional area of an opening of the high-pressure return pipe 8A in response to the excitation current Ri.
The fuel pressure sensor 12 detects the fuel pressure PF in the high-pressure pipe 8.
The ECU 20 not only receives fuel pressure information PF from the fuel pressure sensor 12, but also receives information about the running state from the various sensors 2, performing predetermined computational processes and outputting a calculated control signal to various actuators.
For example, the ECU 20 seeks the mean fuel pressure PFm from the fuel pressure PF detected by the fuel pressure sensor 12 and outputs a control signal which will make the mean fuel pressure PFm match the target fuel pressure PFo.
Next, the mean fuel pressure computing operation according to a conventional fuel injection control assembly for a cylinder-injected engine.
FIG. 14 is a timing chart showing the operation of the fuel pressure detecting process and the averaging process according to a conventional fuel injection control assembly for a cylinder-injected engine.
FIG. 14 shows changes in the injection pulse signal J and the fuel pressure PF over time. In FIG. 14, TC is the calculation cycle for the mean fuel pressure PFm (see dotted chain line) by the ECU 20, and TJ is the length of the injection pulse signal J. t is the fuel pressure detection cycle of the ECU 20, the fuel pressure PF being detected once in each cycle t.
In the waveform of the fuel pressure PF, the white circles represent detected values of fuel pressure PF used to compute the mean, and the black circles represent detected values of fuel pressure PF not used to compute the mean. Because the fuel pressure PF decreases over the time period of the injection pulse duration TJ (when fuel is being injected), the fuel pressure PF detected during this time period (black circles) is eliminated from the calculation of the mean fuel pressure PFm. Moreover, the broken line represents the changes in fuel pressure during fuel shutoff.
First, when the injectors 1F are activated by the injection pulse signal J, fuel is injected by the injectors 1F, and the fuel pressure PF changes as indicated by the solid line in FIG. 14. Moreover, when the injection pulse duration TJ is zero (a fuel shutoff state), the fuel pressure PF increases in response to the discharge operation of the high-pressure fuel pump 7 as indicated by the broken line in FIG. 14.
At that time, in the calculation of the mean fuel pressure PFm, the calculation cycle TC is set in response to the discharge cycle TP of the high-pressure pump 7, and the mean fuel pressure PFm is only calculated from the fuel pressure (PF) detected at time periods other than the fuel injection time period (see white circles).
Consequently, when the injection pulse duration TJ is long, the number of times that fuel pressure PF is detected is insufficient, making calculation of the mean fuel pressure difficult. In running conditions where the load is high, the injection pulse duration TJ is even longer, reducing the opportunities for detecting fuel pressure even further, and in the worst cases, there is a risk that it will not be possible to detect the fuel pressure at all.
Because the discharge cycle TP is reduced as the rotational frequency Ne of the engine increases when the high-pressure pump 7 used is driven by the engine 1 as explained above (see FIG. 13), in the high-revolution region, the number of times that fuel pressure PF is detected during each calculation cycle TC (corresponding to the discharge cycle TP) is reduced.
Because calculation of the weighted mean of the fuel pressure PF detected in each predetermined detection cycle t for each calculation cycle TC as shown in FIG. 14 does not take into consideration the reduction in the number of times that fuel pressure is detected in the high-revolution region, changes in the fuel pressure PF cannot be ascertained accurately, and there is a risk that it will be impossible to calculate the mean fuel pressure PFm.
FIG. 15 is a timing chart showing the fuel pressure detection process and the averaging process when the discharge cycle TP of the high-pressure pump 7 has been shortened by an increase in the engine rotational frequency Ne. In FIG. 15, t1 to t11 are the detection times for the fuel pressure PF.
In this case, the calculation cycle TC for the mean fuel pressure PFm is shorter than in FIG. 14, and the fuel pressure PF detected at times t1, t5, and t6 is used to calculate the mean fuel pressure PFm in the first half of the chart and the fuel pressure PF detected at times t7, t10, and t11 is used to calculate the mean fuel pressure PFm in the second half of the chart.
In other words, in each calculation cycle TC, only three detected values of fuel pressure PF are averaged, making the number of times that fuel pressure PF is detected and used to calculate the average fuel pressure PFm in each calculation cycle TC very small.
As a result, due to the number of times that fuel pressure PF is detected being insufficient, different mean fuel pressures PFm are calculated for the same movements in fuel pressure PF (see dotted chain lines in FIG. 15). Thus, when the engine 1 is running at high-speed and the discharge cycle TP of the high-pressure pump 7 is short, calculation errors for the mean fuel pressure PFm increase, making it difficult to calculate the mean fuel pressure PFm accurately.
In addition, if the excitation current Ri for the high-pressure regulator 10 or the injection pulse duration TJ for the injectors 1F is controlled during sudden changes in the running state of the engine 1 (during transitional running due to acceleration or deceleration) or when the target fuel pressure PFo or the injection timing is altered, the control does not follow the actual changes in fuel pressure PF, and there is a risk that control precision for the injected fuel will deteriorate, causing the air-fuel ratio to deviate from a target value.
As explained above, because a conventional fuel injection control assembly for a cylinder-injected engine does not take into consideration the deleterious effects which changes in the running state and changes in fuel pressure PF have on the precision of the calculation of mean fuel pressure PFm, one problem has been that the time periods in which fuel pressure PF can be detected (time periods other than when fuel is being injected) are extremely short when the engine 1 is in a high-load state, the injection pulse duration TJ is increased, and the fuel injection time period is long, and in the worst cases, it is not possible to calculate the mean fuel pressure PFm at all.